U.S. patent application number 13/021448 was filed with the patent office on 2012-08-09 for directional backlighting for display panels.
This patent application is currently assigned to MICROSOFT CORPORATION. Invention is credited to Timothy Large.
Application Number | 20120200802 13/021448 |
Document ID | / |
Family ID | 46600440 |
Filed Date | 2012-08-09 |
United States Patent
Application |
20120200802 |
Kind Code |
A1 |
Large; Timothy |
August 9, 2012 |
DIRECTIONAL BACKLIGHTING FOR DISPLAY PANELS
Abstract
Various embodiments are disclosed that relate to display panel
backlight systems that output light with a narrower angular
intensity distribution than a diffuse backlight. For example, one
disclosed embodiment provides a backlight system comprising a
wedge-shaped light guide comprising a thin end and a thick end, the
thick end of the wedge-shaped light guide comprising a linear
reflector with plurality of facets, and wherein the backlight
system also comprises a plurality of light sources arranged along
the thin end of the wedge-shaped light guide.
Inventors: |
Large; Timothy; (Bellevue,
WA) |
Assignee: |
MICROSOFT CORPORATION
Redmond
WA
|
Family ID: |
46600440 |
Appl. No.: |
13/021448 |
Filed: |
February 4, 2011 |
Current U.S.
Class: |
349/62 ; 362/606;
362/607; 362/613 |
Current CPC
Class: |
G02B 6/0068 20130101;
G02B 6/0046 20130101; G02B 6/0055 20130101; G02B 6/0073
20130101 |
Class at
Publication: |
349/62 ; 362/613;
362/606; 362/607 |
International
Class: |
G02F 1/1335 20060101
G02F001/1335; F21V 7/22 20060101 F21V007/22 |
Claims
1. A backlight system for a display panel, the backlight system
comprising: a wedge-shaped light guide comprising a thin end and a
thick end, the thick end of the wedge-shaped light guide comprising
a linear reflector with plurality of facets; and a plurality of
light sources arranged along the thin end of the wedge-shaped light
guide.
2. The backlight system of claim 1, wherein the plurality of light
sources are configured to be illuminated together.
3. The backlight system of claim 1, wherein the thin end and the
thick end of the wedge-shaped light guide have a thickness ratio of
0.8:1.8.
4. The backlight system of claim 3, wherein the plurality of facets
have a height of 0.225 mm and an angle of 17.0 degrees with respect
to a plane of the reflector.
5. The backlight system of claim 1, further comprising a plurality
of concentrators, wherein each concentrator is disposed optically
between a corresponding light source and the wedge-shaped light
guide.
6. The backlight system of claim 5, wherein each light source of a
first subset of light sources is configured to output light having
a narrower emitter angle, and wherein each light source of a second
subset of light sources is configured to output light having a
wider emitter angle, and further comprising a controller configured
to switch between operating the backlight system in a narrow angle
mode in which the first subset of light sources are in an on state
and operating the backlight system in a wide angle mode in which
the second subset of light sources are in an on state.
7. The backlight system of claim 1, further comprising a
diffraction grating configured to separate light emitted from the
optical wedge into separate colors, and also further comprising a
lens array configured to direct diffracted light through color
filters of a liquid crystal display panel.
8. The backlight system of claim 5, wherein one or more
concentrators each comprises a cylindrical lens.
9. The backlight system of claim 1, further comprising a turning
structure disposed on an exit surface of the wedge-shaped light
guide and comprising a plurality of facets, wherein angles of the
facets vary as a function of facet position.
10. The light guide of claim 1, wherein the wedge-shaped light
guide comprises a non-planar exit surface.
11. A display device, comprising: a modulating image display panel;
and a backlight system configured to backlight the modulating image
display panel, the backlight system comprising: a wedge-shaped
light guide comprising a thin end and a thick end, the thick end of
the wedge-shaped light guide comprising a linear reflector with
plurality of facets; a plurality of light sources arranged along
the thin end of the backlight system and configured to be
illuminated together; and a turning structure disposed on an exit
surface of the wedge-shaped light guide to redirect light emitted
from the exit surface of the wedge-shaped light guide, the turning
structure comprising a plurality of facets each having an angle
with respect to a turning structure surface normal, wherein the
angles of the facets vary as a function of facet position on the
turning structure.
12. The display device of claim 11, wherein the thin end and the
thick end of the wedge-shaped light guide have a thickness ratio of
0.8:1.8.
13. The display device of claim 12, wherein the plurality of facets
have a height of 0.225 mm and an angle of 17.0 degrees with respect
to a plane of the reflector.
14. The display device of claim 11, further comprising a plurality
of concentrators, wherein each concentrator is disposed optically
between a corresponding light source and the wedge-shaped light
guide.
15. The display device of claim 14, wherein each light source of a
first subset of light sources has a corresponding concentrator
configured to emit light at a narrower emitter angle, and wherein
each light source of a second subset of light sources is configured
to emit light at a wider emitter angle.
16. The display device of claim 15, further comprising a controller
configured to switch between operating the backlight system in a
narrow angle mode in which the first subset of light sources are in
an on state and operating the backlight system in a wide angle mode
in which the second set of light sources are in an on state.
17. The display device of claim 2, wherein the plurality of light
sources are configured to emit light from the light sources having
an angular distribution with a full-width half-maximum of between
40 and 80 degrees.
18. A method of operating a backlit display device, comprising:
illuminating a plurality of light sources to inject light into a
thin end of an wedge-shaped light guide at multiple locations along
a length of the thin end of the wedge-shaped light guide;
internally reflecting the light via a linear reflector disposed at
a thick end of the wedge-shaped light guide; emitting the light
from the wedge-shaped light guide; and directing the light emitted
from the light guide through a modulating display panel to produce
a displayed image.
19. The method of claim 3, further comprising directing light from
each light source through a concentrator before injecting the light
into the wedge-shaped light guide.
20. The method of claim 19, wherein the plurality of light sources
is a first plurality of light sources, and wherein the method
further comprises switching the first plurality of light sources
off and switching on a second plurality of light sources on upon
occurrence of a triggering event, wherein light from each of the
second plurality of light sources is injected to the wedge-shaped
light guide with a wider angular intensity distribution than light
from each of the first plurality of light sources.
Description
BACKGROUND
[0001] Display devices, such as laptop computers, tablet computers,
slate computers, smart phones, and the like, may use a modulating
display panel, such as a liquid crystal display, in combination
with a backlight to display images to users. Various backlights are
known for such display devices. Some backlight sources, such as
light-emitting diodes, are used in combination with a diffuser to
distribute light with an acceptably uniform intensity, while
others, such as electroluminescent panels, may provide a suitably
uniform intensity without a diffuser. Such backlights generally
output light having a broad intensity distribution. As a result, a
relatively large luminous flux may be output at potentially high
angles relative to a normal of the display panel surface plane.
SUMMARY
[0002] Various embodiments are disclosed that relate to display
panel backlight systems that output light with a narrower angular
intensity distribution than a diffuse backlight. For example, one
disclosed embodiment provides a backlight system comprising a
wedge-shaped light guide comprising a thin end and a thick end, the
thick end of the wedge-shaped light guide comprising a linear
reflector with plurality of facets, and also comprising a plurality
of light sources arranged along the thin end of the light
guide.
[0003] This Summary is provided to introduce a selection of
concepts in a simplified form that are further described below in
the Detailed Description. This Summary is not intended to identify
key features or essential features of the claimed subject matter,
nor is it intended to be used to limit the scope of the claimed
subject matter. Furthermore, the claimed subject matter is not
limited to implementations that solve any or all disadvantages
noted in any part of this disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIG. 1 shows an embodiment of a backlit display device in
the form of a laptop computer.
[0005] FIG. 2 shows a schematic depiction of a side view of an
embodiment of a backlight system and a modulating display
panel.
[0006] FIG. 3 shows a schematic depiction of a top view of the
backlight system embodiment of FIG. 2.
[0007] FIG. 4 shows a schematic depiction of an embodiment of a
faceted end reflector for the light guide of the embodiment of FIG.
2.
[0008] FIG. 5 shows an embodiment of a concentrator comprising a
cylindrical lens.
[0009] FIG. 6 shows an angular intensity distribution of light
emitted at each of a plurality of test locations for an embodiment
of a backlight system.
[0010] FIG. 7 shows an angular intensity distribution of light
emitted at each of a plurality of test locations for another
embodiment of a backlight system.
[0011] FIG. 8 shows an embodiment of a backlight system comprising
a first subset of light sources configured to emit light with a
wider angular intensity distribution, and a second subset of light
sources configured to emit light with a narrower angular intensity
distribution, and illustrates light being emitted by the first
subset of light sources.
[0012] FIG. 9 illustrates light being emitted by the second subset
of light sources of the embodiment of FIG. 8.
[0013] FIG. 10 shows a flow diagram depicting an embodiment of a
method of operating a backlit display device.
[0014] FIG. 11 shows an embodiment of a turning structure.
[0015] FIG. 12 shows a side view of a plurality of facets of the
embodiment of FIG. 11.
[0016] FIG. 13 shows another embodiment of a turning structure.
[0017] FIG. 14 shows a schematic depiction of an embodiment of a
computing device.
[0018] FIG. 15 shows a schematic depiction of an embodiment of a
color filter matching backlight system.
[0019] FIG. 16 shows a schematic depiction of light rays traveling
through the embodiment of FIG. 15.
[0020] FIG. 17 shows a graph illustrating a modeling of intensity
as a function of position for one color of light from the
embodiment of FIG. 15.
DETAILED DESCRIPTION
[0021] As mentioned above, conventional backlights for modulating
display panels often output light having a broad intensity
distribution. Such backlights may allow displayed images to be
viewed from a wide range of angles. However, some display devices,
including but not limited to laptop computers, are often used by
one user at a time facing the screen directly. Thus, light directed
out of the display panel at high angles to the screen normal may be
wasted in such devices. The production of such wasted light may
impact battery life. Further, in some situations, such as while
working on potentially confidential matters and/or in close
proximity to strangers (e.g. while on an airplane), it may be
desirable for displayed images not to be visible at high angles to
help maintain privacy.
[0022] Thus, various embodiments are disclosed herein that relate
to the backlighting of display panels via light having a narrower
angular intensity distribution than diffuse backlighting. The
disclosed embodiments also may have a wider angular light intensity
distribution than a collimated source, thereby permitting some
level of off-axis viewing where it is desired to share an image
with another.
[0023] FIG. 1 shows an embodiment of a display device in the form
of a laptop computer 100 having a backlit display panel 102. It
will be understood that laptop computer 100 is depicted for the
purpose of example, and that the embodiments described herein may
be used with any suitable display device, including but not limited
to notepad computers, tablet computers, slate computers, smart
phones and other portable phones, portable media players, computer
monitors, televisions, etc.
[0024] FIG. 2 shows a schematic side view of an embodiment of a
backlight system 200 for a display panel 201 and FIG. 3 shows a
schematic top view of backlight system 200. It will be understood
that the relative sizes of structural features shown in FIG. 2 are
exaggerated for the purpose of illustration, and are not intended
to be limiting. Backlight system 200 comprises a wedge-shaped light
guide 202 having a thin end 204 and a thick end 206. Thin end 204
comprises a light input interface configured to receive light
injected by a plurality of light sources 208, such as the depicted
light-emitting diodes or other suitable light sources. Thick end
206 comprises a linear reflector 210 configured to change the angle
of internally reflected light from light sources 208 and to direct
the light toward a light exit interface 212 such that the light
exits the light exit interface 212 at or above a critical angle of
reflection. The term "linear reflector" refers to a reflector that
is not curved in a dimension along a width of the wedge. A wedge
having such a reflector may be formed from a linear extrusion, as
explained in more detail below, or may be formed in any other
suitable manner, such as injection molding. A turning structure 214
may be used to redirect light emitted by the front of the light
guide 202 to a weak diffuser and then through the display panel
201. Light emitted from the back of the light guide is turned by a
reflector and returned to the front. The reflector can for example
be metalized polyester sheet, prismatic reflector, or multilayer
dielectric coated sheet.
[0025] The backlight system 200 utilizes a plurality of light
sources 208 illuminated together, rather than a single light
source, because the light guide 202 is non-imaging. As shown in
FIG. 3, the plurality of light sources 208 are arranged along the
thin end 204 of the light guide 202 such that light from each light
source 208 fans out and overlaps as it propagates through the light
guide. The use of a sufficient number of light sources 208 based
upon the angular distribution of the diffuser may allow the
production of a backlight with a suitably uniform intensity across
the area of the exit interface 212.
[0026] The use of the linear reflector 210 may offer various
advantages. For example, manufacturing a wedge-shaped light guide
202 with a reflector that is a linear extrusion may be easier and
less expensive than manufacturing an imaging wedge-shaped light
guide having a toroidal reflector. This is because the wedge with
the linear reflector may be formed from linear extruding and
polishing, without any machining to form the reflector shape. In
contrast, a toroidal reflector may require machining after
extruding to form a desired reflector shape. Further, the linear
reflector allows a wedge to have a perimeter that is the same as or
just slightly larger than a corresponding LCD panel. In contrast, a
wedge having a toroidal reflector extends beyond the perimeter of a
corresponding LCD panel due to the curvature of the reflector.
[0027] Light guides of the design described herein have a thickness
that is limited by the size of the LED illuminating the thin end of
the light-guide. For example, in one specific embodiment, the light
guide 202 has a 0.8/1.8 ratio of thin end/thick end thickness, and
has a maximum thickness of 1.8 mm, for a maximum backlight system
target thickness of 2 mm including a turning structure thickness of
160 microns. Such a light guide is matched to standard 3806 side
emitting LEDs (3.8.times.0.6 mm package size). It will be
understood that these dimensions are presented for the purpose of
example, and are not intended to be limiting
[0028] The light guide 202 may be formed in any suitable manner
that yields a surface with a desired smoothness. For a thin light
guide for a laptop computer, for example, it is advantageous to
form the part by injection molding. For example, roughness averages
of the order 1 nm and light transmission of 90% per meter may be
achievable by molding material such as poly(methyl methacrylate)
(PMMA). It will be understood that these specific embodiments are
described for the purpose of illustration and are not intended to
be limiting in any manner, as any suitable material may be used to
form a light guide having any suitable smoothness and
transmissivity.
[0029] The reflector 210 may be formed without machining, for
example by injection molding. In injection molding, polymer enters
a cavity which is reverse of the desired form. Typically the cavity
will comprise the light exit face 212 and the opposing major
surface, and the facetted reflector 210. Plastic enters the
injection mold cavity through the thin end 204. Once the plastic
has frozen, the part is removed from the injection mold tool and
the gate material that remains along face 204 is removed and the
face is machined and polished or laser cut so that it is
smooth.
[0030] In some embodiments, as shown in FIG. 4, the reflector 210
may comprise a plurality of facets 400. The use of a faceted
reflector may help to avoid modulation of light near the reflector
end. The facets 400 may have any suitable dimensions. For example,
in embodiments where the thin/thick end ratio is 0.8/1.8, the
reflector may have eight facets each having a height of 0.225 mm
and an angle of 17.0 degrees with respect to an end plane of the
light guide. It will be understood that these values are presented
for example, and are not intended to be limiting in any manner.
[0031] In some embodiments, a concentrator may be used to
concentrate light from each light source for injection into the
light guide 202. Any suitable concentrator design may be used. For
example, an LED light source may be formed from a LED embedded in
an optically transmissive material. In such embodiments, a
concentrator may be formed by forming cutouts in the transmissive
material such that the interface between air and the transmissive
material created by the cutouts defines a desired emitter angle
and/or beam shape by total internal reflection. Such concentrator
designs increase the apparent source size while reducing the range
of emitted angles. Such devices are disclosed, for example, in the
book "High Collection Non Imaging Optics" by Welford and Winston,
published in 1989.
[0032] In another embodiment, the concentrator shapes are cut or
directly molded into the thin face of the light-guide 202, and the
LEDs are soldered to a flexible PCB strip. The LED strip is then
butted up against the light guide 202.
[0033] In other embodiments, a concentrator external to the LED
packaging may be used. FIG. 5 depicts an example embodiment of such
a concentrator 500 in the form of a cylindrical lens that acts as a
horizontal collimator (e.g. where the light is concentrated in a
direction along the thin end of the light guide 202). An angular
distribution of light from such a concentrator may be determined by
a radius and conic constant of the cylindrical lens. Such lenses
may be made in strips, allowing for efficient manufacturing and
installation. Light may be coupled into the light guide 202 from
concentrator 500 by bounding a top and a bottom of the interface
between the concentrator and the wedge with reflective strips, for
example.
[0034] Light guide 202 may have any suitable dimensions, including
but not limited to the specific examples given above. One
embodiment of a method of designing light guide 202 for a specific
application is as follows. First, a size and maximum thickness of
light guide 202 is selected based upon a desired end use. These
quantities may take into account factors such as a turning
structure thickness, display panel thickness, and other such
geometric factors. Next, a power budget may be calculated based
upon a desired output intensity. Calculating a power budget may
take into account factors such as light source intensities, display
panel transmission and loss factors, turning film losses, light
guide loss factors (e.g. light guide material losses due to
absorption, back reflections from the turning structure,
reflections from the linear reflector, etc.), and light source
coupling losses, and may help to determine how many and what type
of light sources to utilize.
[0035] After determining a power budget, a concentrator may be
designed based upon a desired horizontal light source angle, and
modeling software such as ZEMAX, available from the Zemax
Development Corporation of Bellevue, Wash., may be used to optimize
the light distribution by modifying the reflector facet angle and
the ratio of the thicknesses of the thin and thick end of the
light-guide. The distribution of illuminance on the exit face is
calculated by ray tracing. The distribution may be widened by
changing the thickness ratio and centered by changing the facet
angles in the reflector. It has been found that a thickness ratio
of 0.8:1.8 and a facet angle of 17 degrees (relative to the center
plane of the light guide) are suitable in one embodiment. In
general, the light exit surface and opposing surface may be
configured to be planar. However, he light output distribution may
be further flattened by changing surface spatial frequency
components of the light exit surface and opposing major face. The
distribution may be flattened further by modifying an input
geometry. Once a suitable light guide structure is identified via
such modeling, a prototype may be constructed and tested via
13-point conoscopic testing or the like to determine a uniformity
of the light emitted from the backlight system at different points
across the backlight output. The design modification processes may
then be performed iteratively to achieve a product design having
desired optical properties.
[0036] FIGS. 6 and 7 show graphs that illustrate luminance as a
function of viewing angle at a plurality of locations across the
light exit surface of the light guide. The data illustrated in
these figures was gathered via 13-point conoscopic ray tracing of a
wedge-shaped light guide having planar major surfaces, a 0.8/1.8
thin/thick ratio, and a rear reflector having the configuration
described above with reference to FIG. 4. The data in FIG. 6 was
gathered via a narrow angle configuration that utilized 16 LEDs
spaced at 21.4 mm intervals along the thin edge of a 15.6''
diagonal, 16:9 format backlight, coupling light into concentrator
structures cut into the backlight. The data in FIG. 7 was gathered
via a second wide angle configuration that utilized 32 LEDs spaced
between the first set of 16 in groups of 2, without concentrator
structures. The depicted curves show angular intensity variation in
a horizontal direction transverse to an optical axis of the light
guide. It will be understood that intensity variation in the
vertical direction may be substantially similar in both designs
where the light sources have a similar vertical emitter angle.
[0037] First referring to FIG. 6, the narrow angle configuration
was found to have a luminance uniformity of approximately 84%. Next
referring to FIG. 7, the wide angle configuration was found to have
a luminance uniformity of approximately 74%. In either case, such
uniformity may be sufficient for use with display panels for
laptop, notebook, notepad, slate, etc. computing devices, for which
a uniformity of >60% may be desirable.
[0038] The wide angle and narrow angle configurations may be used
together in a dual mode backlight system that can switch between
the configurations under various circumstances. FIGS. 8 and 9
illustrate an embodiment of such a dual mode backlight system 800
having a first subset of light sources configured to output light
with a narrower angle and a second subset of light sources
configured to output light with a wider angle. In these figures,
the first subset of light sources 802 are shown as LEDs each having
a corresponding concentrator 804, while the second subset of light
sources 806 are shown as LEDs without concentrators. It will be
understood that, in other embodiments, both subsets of light
sources may utilize concentrators having different output angles.
Further, it will be understood that any other suitable light source
than LEDs may be used. While LEDs of the first and second subsets
of light sources are shown in an alternating configuration in FIGS.
8 and 9, it will be understood that the first and second plurality
of light sources may have any suitable arrangement relative to one
another, and also may each have any suitable number of individual
light sources. Further, while described in the context of a dual
mode system, it will be understood that a backlighting system may
have any suitable number of subsets of light sources to enable any
suitable number of backlighting modes.
[0039] Backlight system 800 further comprises a controller 810.
Controller includes a data-holding subsystem 812 configured to hold
machine-readable instructions, and a logic subsystem 814 configured
to execute the instructions stored in the data-holding subsystem to
switch between a narrow angle mode and in a wide angle mode upon
occurrence of a triggering event. The controller 810 may take the
form of a dedicated on-board controller that is contained within
the display system enclosure, a dedicated controller built in to a
related device (e.g. located on a motherboard of a computing device
that incorporates the backlight system), or may have any other
suitable configuration. Further, it will be understood that the
backlight system 800 may be in communication with other components
(not shown in FIGS. 8-9) of a computing device that controls the
backlight system. For example, the controller 810 may receive
instructions from a processor or other logic components of a
computing device to which the backlight system controller is
coupled, such that the processor or other logic components can
trigger an automated switch between a narrow angle mode and a wide
angle mode.
[0040] FIG. 8 depicts operation of the dual mode backlight system
800 in a narrow angle mode. In this mode, the first subset of light
sources 806 are operated in an on state, while the second subset of
light sources 802 are operated in an off state. In this mode, the
light emitted from a display screen has a narrower horizontal
angular luminance distribution, thereby helping to maintain privacy
and conserve battery life. Next, FIG. 9 depicts operation of the
dual mode backlight system 800 in a wide angle mode in with the
first and second subsets are respectively operated in off and on
states. In this mode, the light emitted from a display screen has a
wider horizontal angular luminance distribution than that of the
narrow angle mode, but still narrower than a conventional
backlight.
[0041] Where the narrow and wide angle modes respectively have the
angular luminance distributions shown in FIGS. 6-7, the narrow
angle mode may have a full-width half-maximum (FWHM) of
approximately 40-45 degrees, while the wide angle mode may have a
FWHM of approximately 70-80 degrees. With these luminance
distributions, the narrow angle mode may utilize 1/3 of the power
of a conventional backlight system, while the wide angle mode may
utilize 2/3 of the power of a conventional backlight system, where
the conventional backlight system is one utilizing prismatic
brightness enhancement films.
[0042] As a more specific example, referring to the specific
configurations described with reference to FIGS. 6-7, by switching
on narrow angle subset of 16 LEDs, the user has a substantially
private view. By switching on the wide angle subset of 32 LEDs, a
public view is obtained. When both subsets of LEDs are lit, the
view is both public and high brightness in the centre of the
viewing cone, which may for example be useful in high ambient
lighting situations. The power consumption in private mode of this
embodiment may be significantly lower than a conventional backlight
unit, potentially by a factor of 3-5 depending on the design of the
conventional backlight unit to which it is compared.
[0043] Backlight system 800 may be configured to switch between the
wide angle mode and the narrow angle mode based upon any suitable
triggering event. Examples include, but are not limited to, manual
user selection and automated triggering. For example, a user may
wish to utilize a narrow angle mode as a default setting to
conserve power and maintain privacy, but manually switch to a wide
angle mode for shared viewing of images displayed on the display
panel. Likewise, a computing device may include machine-readable
instructions executable by a logic subsystem of a computing device
to switch the viewing mode from the wide angle viewing mode to the
narrow angle viewing mode based upon the occurrence of a triggering
event during execution of a program. As a more specific example,
such instructions may be executable to detect a user browsing from
a non-secure web page to a secure web page, and may in response
change from a wide angle mode to a narrow angle mode. It will be
understood that this specific embodiment is presented for the
purpose of example, and is not intended to be limiting in any
manner.
[0044] FIG. 10 shows an embodiment of a method 1000 of operating a
backlit display device. Method 1000 comprises, at 1002,
illuminating a plurality of light sources to inject light into a
thin end of a wedge-shaped light guide at multiple locations along
a length of the thin end of the wedge-shaped light guide, and at
1004, internally reflecting the light via a reflector disposed at a
thick end of the wedge-shaped light guide. In some embodiments, as
shown at 1003, light may be directed through a concentrator before
being introduced into the light guide. Next, method 1000 comprises,
at 1006, emitting the light from the wedge-shaped light guide, and
at 1008, directing the light emitted from the light guide through a
modulating display panel to produce a displayed image.
[0045] As described above, in some instances, the plurality of
light sources may be a first plurality of light sources, and a
backlighting system may at least a second plurality of light
sources in which each light source is configured to inject light
into the light guide with a wider angular intensity distribution
than that of the first plurality of light sources. As such, method
1000 optionally comprises, at 1010, switching the first plurality
of light sources off and switching the second plurality of light
sources on upon occurrence of a triggering event. The triggering
event may be any suitable event, including but not limited to a
user request to manually switching viewing modes and/or events
detected automatically by software, firmware and/or hardware.
[0046] In some embodiments, a turning structure having a changing
facet angle as a function of position may be utilized in
combination with a cylindrically reflecting wedge-shape light guide
to form an imaging system. FIG. 11 shows a schematic view of an
example embodiment of an imaging turning structure 1100 configured
to be used with a cylindrically reflecting wedge-shape light guide,
and FIG. 12 shows a schematic side view of facets of the imaging
turning structure. The facet angle of the turning structure 1100,
illustrated as angle D in FIG. 12, varies smoothly from point A to
point C of FIG. 11, with point B signifying a midpoint. The facet
angles may vary between any suitable values. For example, in some
embodiments, the facet angles may vary between 50 and 57 degrees,
with the angle at point B being 53.5 degrees. It will be understood
that these values are presented for the purpose of example, and are
not intended to be limiting in any manner.
[0047] The facets of turning structure 1100 extend in a straight
line along a long dimension of the turning structure 1100. FIG. 13
shows another embodiment of an imaging turning structure 1300
comprising facets arranged in a circular pattern. As with turning
structure 1100, the facets of turning structure 1300 vary across
the turning structure. In some embodiments, the facets may vary
between 50 and 57 degrees between points A and C, and have a value
of 53.5 at midpoint B. In other embodiments, the facets may have
any other suitable values.
[0048] The turning structures 1100 and 1300 may have any suitable
thicknesses and may be formed in any suitable manner. For example,
in some embodiments the turning structures have a thickness of 0.65
microns, and are formed by linear extrusion (turning structure
1100) or by reel to reel replication (turning structure 1100 or
1300), or by hot pressing (turning structure 1100 or 1300). It will
be understood that these specific embodiments are described for the
purpose of example, and are not intended to be limiting in any
manner.
[0049] As mentioned above, in some embodiments, the major faces of
a cylindrically reflecting wedge-shaped light guide (e.g. the light
exit interface and the opposite face) may be non-planar to help
improve illuminance uniformity. The profile of such a light guide
may be determined in any suitable way. One example embodiment is as
follows. First, an angular optical power distribution at desired
angular increments (such as 0.1 of a degree) of the light relative
to the optical axis of the light guide may be determined (a) at the
exit of the light source, (b) inside of the light guide before the
end reflector, and (c) inside of the light guide after the end
reflector. The distribution inside of the light guide before the
reflector will be narrower than the distribution at the exit of the
light source due to Snell's law. Also, as the light guide thickness
may increase by a factor of approximately two from the thin end to
the thick end, by the equivalence of index to thickness theorem,
the injection of light into the wedge-shaped light guide is similar
in effect to injecting light into a guide of double the refractive
index as the actual light guide refractive index. The end reflector
offsets the distribution within the light guide by twice its angle
relative to an end plane of the reflector.
[0050] The thickness of the light guide at any point is determined
by the change in angle of a ray. Given that t*sin(theta) is a
constant, the point at which any given ray of angle theta
originating from the linear reflector exits the light guide may be
determined. The distance between two rays is set by the power
density. In order to get uniform illuminance on the light guide
surface, the distance between two neighboring rays is proportional
to the power density in angle space. The total distance to the ray
exit point is therefore proportional to the integral of the power
density. The rays exiting first are those with the highest angle at
the reflector. From this, light guide thickness and distance as a
function of ray angle may be determined. Then, thickness and
distance may be plotted against one another to determine a light
guide profile that produces a flat power distribution on exit from
the guide. It will be noted that variations from planarity of +/-15
microns may be sufficient to increase the uniformity of the
wedge-shaped light guide.
[0051] As mentioned above, in some embodiments, the disclosed
backlight systems and backlighting methods may be tied to a
computing system including one or more computers. In particular,
the methods and processes described herein may be implemented as a
computer application, computer service, computer API, computer
library, and/or other computer program product.
[0052] FIG. 14 schematically shows a nonlimiting computing system
1400 that may perform one or more of the above described methods
and processes. Computing system 1400 is shown in simplified form.
It is to be understood that virtually any computer architecture may
be used without departing from the scope of this disclosure. In
different embodiments, computing system 1400 may take the form of a
mainframe computer, server computer, desktop computer, laptop
computer such as that shown in FIG. 1, tablet computer, home
entertainment computer, network computing device, mobile computing
device, mobile communication device, gaming device, etc.
[0053] Computing system 1400 includes a logic subsystem 1402 and a
data-holding subsystem 1404. Computing system 1400 also includes a
display subsystem 1406, and/or other components not shown in FIG.
14, such as a communication subsystem, user input devices such as
keyboards, mice, game controllers, cameras, microphones, and/or
touch screens, for example.
[0054] Logic subsystem 1402 may include one or more physical
devices configured to execute one or more instructions. For
example, the logic subsystem 1402 may be configured to execute one
or more instructions that are part of one or more applications,
services, programs, routines, libraries, objects, components, data
structures, or other logical constructs. Such instructions may be
implemented to perform a task, implement a data type, transform the
state of one or more devices, or otherwise arrive at a desired
result.
[0055] The logic subsystem 1402 may include one or more processors
that are configured to execute software instructions. Additionally
or alternatively, the logic subsystem 1402 may include one or more
hardware or firmware logic machines configured to execute hardware
or firmware instructions. Processors of the logic subsystem 1402
may be single core or multicore, and the programs executed thereon
may be configured for parallel or distributed processing. The logic
subsystem may optionally include individual components that are
distributed throughout two or more devices, which may be remotely
located and/or configured for coordinated processing. One or more
aspects of the logic subsystem may be virtualized and executed by
remotely accessible networked computing devices configured in a
cloud computing configuration.
[0056] Data-holding subsystem 1404 may include one or more
physical, non-transitory, devices configured to hold data and/or
instructions executable by the logic subsystem to implement the
herein described methods and processes. When such methods and
processes are implemented, the state of data-holding subsystem 1404
may be transformed (e.g., to hold different data).
[0057] Data-holding subsystem 1404 may include removable media
and/or built-in devices. Data-holding subsystem 1404 may include
optical memory devices (e.g., CD, DVD, HD-DVD, Blu-Ray Disc, etc.),
semiconductor memory devices (e.g., RAM, EPROM, EEPROM, etc.)
and/or magnetic memory devices (e.g., hard disk drive, floppy disk
drive, tape drive, MRAM, etc.), among others. Data-holding
subsystem 1404 may include devices with one or more of the
following characteristics: volatile, nonvolatile, dynamic, static,
read/write, read-only, random access, sequential access, location
addressable, file addressable, and content addressable. In some
embodiments, logic subsystem 1402 and data-holding subsystem 1404
may be integrated into one or more common devices, such as an
application specific integrated circuit or a system on a chip.
[0058] FIG. 14 also shows an aspect of the data-holding subsystem
in the form of removable computer-readable storage media 1408,
which may be used to store and/or transfer data and/or instructions
executable to implement the herein described methods and processes.
Removable computer-readable storage media 1408 may take the form of
CDs, DVDs, HD-DVDs, Blu-Ray Discs, EEPROMs, and/or floppy disks,
among others.
[0059] It is to be appreciated that data-holding subsystem 1404
includes one or more physical, non-transitory devices. In contrast,
in some embodiments aspects of the instructions described herein
may be propagated in a transitory fashion by a pure signal (e.g.,
an electromagnetic signal, an optical signal, etc.) that is not
held by a physical device for at least a finite duration.
Furthermore, data and/or other forms of information pertaining to
the present disclosure may be propagated by a pure signal.
[0060] The terms "software," "firmware" and "program" may be used
to describe an aspect of computing system 1400 that is implemented
to perform one or more particular functions. In some cases, such a
module, program, or engine may be instantiated via logic subsystem
1402 executing instructions held by data-holding subsystem 1404. It
is to be understood that different modules, programs, and/or
engines may be instantiated from the same application, service,
code block, object, library, routine, API, function, etc. Likewise,
the same module, program, and/or engine may be instantiated by
different applications, services, code blocks, objects, routines,
APIs, functions, etc. The terms "module," "program," and "engine"
are meant to encompass individual or groups of executable files,
data files, libraries, drivers, scripts, database records, etc.
[0061] It is to be appreciated that a "service", as used herein,
may be an application program executable across multiple user
sessions and available to one or more system components, programs,
and/or other services. In some implementations, a service may run
on a server responsive to a request from a client.
[0062] Display subsystem 1406 may be used to present, via the
backlighting system embodiments disclosed herein, a visual
representation of data held by data-holding subsystem 1404. As the
herein described methods and processes change the data held by the
data-holding subsystem, and thus transform the state of the
data-holding subsystem, the state of display subsystem 1406 may
likewise be transformed to visually represent changes in the
underlying data. Display subsystem 1406 may include one or more
display devices combined with logic subsystem 1402 and/or
data-holding subsystem 1404 in a shared enclosure, or such display
devices may be peripheral display devices.
[0063] In some embodiments, a backlight system according to the
present disclosure may be used in conjunction with diffractive
optics to separate white backlighting into colored light to be
directed through color filters of an LCD panel. Such a system may
be referred to as a color matching backlighting system. FIG. 15
shows a schematic depiction of an embodiment of such a color
matching backlight system 1500. The color matching backlight system
1500 includes a plurality of light sources 1502 configured to
direct light into an optical wedge 1504, such as an optical wedge
having a linear rear reflector as described above. After emerging
from the optical wedge 1504, light is directed through a
diffracting lens array 1506 comprising a plurality of lenses 1507
and a diffraction grating, illustrated schematically for one lens
1507 as a location 1508 at which light is diffracted into colored
bands (represented by different line formats in FIG. 15). The
diffraction grating may be at any suitable location within or on
the lens array 1506, and may be located in front of, behind, or
within the lenses 1507 of the lens array 1506. Further, in some
embodiments, the diffraction grating may be separate from the lens
array 1506.
[0064] The diffracting lens array 1506 separates white light from
each light source into constituent bands of color, and then directs
the light through the color filters 1510 of the pixels 1512 of an
LCD panel. FIG. 15 illustrates light from three light sources
entering a single lens 1507/diffraction grating segment of the
diffracting lens array 1506. This light is diffracted into colored
bands (represented by different line formats in FIG. 15), and then
is directed through color filters of three pixels of the LCD screen
(illustrated as three sets of color filters).
[0065] Next, FIG. 16 illustrates that the diffracting lens array
1506 produces multiple images of each light source. Thus, the
images of the different light sources may be made to overlap,
thereby producing an acceptably uniform intensity across the LCD
panel. In FIG. 16, rays from a first image source are illustrated
at 1600, and rays from a second image source are illustrated at
1602. From FIG. 16, it can be seen that the image of the light
source represented by rays 1600 and images of the light source
represented by rays 1602 may be configured to overlap via selection
of the pitch of the lens array and focal length of the lenses in
the lens array. By diffracting this light and directing the
resulting colors through the color filters of the LCD panel, color
matching backlight system 1500 may increase light throughput
relative to a backlight system that illuminates an LCD panel with
white light, as less total light power is filtered by the LCD color
filters due to the color matching. It will be understood that a
diffuser may be placed over the LCD to form an image plane for
viewing images produced by the LCD.
[0066] It is to be further understood that the configurations
and/or approaches described herein are exemplary in nature, and
that these specific embodiments or examples are not to be
considered in a limiting sense, because numerous variations are
possible. The specific routines or methods described herein may
represent one or more of any number of processing strategies. As
such, various acts illustrated may be performed in the sequence
illustrated, in other sequences, in parallel, or in some cases
omitted. Likewise, the order of the above-described processes may
be changed.
[0067] The subject matter of the present disclosure includes all
novel and nonobvious combinations and subcombinations of the
various processes, systems and configurations, and other features,
functions, acts, and/or properties disclosed herein, as well as any
and all equivalents thereof.
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